Lubricant for controlled-slip differential

ABSTRACT

AN IMPROVED METHOD OF LUBRICATION OF A CONTROLLED-SLIP DIFFERENTIAL COMPRISES USING A LUBRICANT COMPRISING (A) SYNTHETIC SULFURIZED OIL CONSISTING ESSENTIALLY OF A SULFURIZED BLEND OF LARD OIL AND A C12-24 MONOOLEFIN AND (B) A HYDROCARBON BASE STOCK HAVING A KINEMATIC VISCOSITY AT 210*F. IN THE RANGE OF 1.5-200.0 CS. AND CONTAINING AT BLEND OF AT LEAST ONE C13-C29 NAPHTHENE AND FORM 0.120 PARTS BY WEIGHT, BASED ON SAID NAPHTHENE OF AT LEAST ONE MEMBER FROM AT LEAST ONE OF THE FOLLOWING GROUPS (A), (B), (C) AND (D): (A) A SYNTHETIC LIQUID C3-C4 OLEFIN HOMOPOLYMER COPOLYMER, OR TERPOLYMER; (B) A MEMBER FROM GROUP (A) ABOVE WHICH IS AT LEAST PARTIALLY HYDROGENATED; (C) A SEVERLY HYDROREFINED NAPHTHENIC LUBE CONTAINING LESS THAN 1% OF GEL AROMATIC HYDROCARBONS; AND (D) A SEVERLY HYDROREFINED PARAFFINIC LUBE CONTAINING LESS THAN 1% OF GEL AROMATIC HYDROCARBONS; AND WHEREIN THE AMOUNT OF SAID BLEND WHICH IS PRESENT IN SAID BASE STOCK IS SUFFICIENT TO PROVIDE A GREATER COEFFICIENT OF TRACTION, MEASURED T 600 F./MIN., 200*F., 400,000 P.S.I., THAN WOULD BE PROVIDED BY SUBSTITUTION OF THE SAME AMOUNT OF ASTM OIL NO. 3 FOR SAID BLEND IN SAID BASE STOCK AND WHEREIN SAID LUBRICANT CONTAINS 0.5-10 VOLUMES OF SYNTHETIC SULFURIZED OIL FOR EACH 100 VOLUMES OF SAID BASE STOCK. THE PREFERRED LUBRICANT ALSO CONTINS AN EXTREME PRESSURE ADDITIVE (E.G. TRICRESYL PHOSPHATE) AND AN ADDITIVE WHICH LOWERS THE STATIC FRICTION OF THE LUBRICANT (E.G. A SURFACE-ACTIVE, ORGANIC PHOSPHATE ESTER OF A LINEAR ALIPHATIC, ETHOXYLATED ALCOHOL).

y 23, 1974 T. o. NEWINGHAM ETAL 3,825,495

LUBRICANT FOR CONTROLLED-SLIP DIFFERENTIAL Filed Feb 19, 1971 CONTROLLED-SLIP DIFFERENTIAL INVENTORS THOMAS D. NEWINGHAM ALEXANDER D. RECCHUITE JOHN Q. GRIFFITH III MARCUS W. HASELTINE JR ATTORN E Y United States Patent- "Office 3,825,495 Patented July 23, 1974 3,825,495 v Y i. 1 LUBRICANT FOR CONTROLLED-SLIP DIFFERENTIAL Thomas D. Newingham, Broomall, and Alexander D.

Recchuite, Boothwyn, Pa -John Q. Griflith III, Claymont, Del., and Marcus W. Haseltine, Jr., Brookhaven, Pa., assignors to Sun Research and Development Co., Philadelphia, Pa. Filed Feb. 19, 1971, Ser. No. 116,985

Int. Cl. Cm 1/48, N38

US. Cl.252.,32.7 E 11 Claims ABSTRACT OF THE DISCLOSURE (a) a synthetic liquid C -C olefin homopolymer copolymer, or terpolymer;

'(b) a member from group (a) above which is at least partially hydrogenated;

'(c) a severely hydrorefined naphthenic lube containing less than 1% of gel aromatic hydrocarbons; and

(d) a severely hydrorefined paraflinic lube containing less than 1% of gel aromatic hydrocarbons;

andwherein the amount of said blend which is present in said base stock is sufficient to provide a greater coefficient of traction, measured at 600 ft./min., 200 R, 400,000 p.s.i., than would be provided by substitution of the same amount of ASTM Oil No. 3 for said blend in said base stock and wherein said lubricant contains 0.5-10 volumes of synthetic sulfurized oil for each 100 volumes of said base stock. The preferred lubricant also contains an extreme pressure additive (e.g. tricresyl phosphate) and an additive which lowers the static friction of the lubricant (e.g. a surface-active, organic phosphate ester of a linear aliphatic, ethoxylated alcohol).

CROSS REFERENCES TO RELATED APPLICATIONS The present application is related to the following listed applications:

Filing date Tltlelinventofls) Blending Branched Parafl'in Fluids for Use in Traction Drive Transmisslon-Irl N. Duling-David S. Gates and Marcus W. Haseltine.

Serial No.

679,834 (now U.S. 3,595 ,719)7, issued 679,851 (new U.S. Traction Drive Transmission Con- 3,598,740,issued talning Paraflinic oil as Lubri- 8-10-71). cant-Irl N. Duling-David S. Gates and Thomas D. Newlngharn. 7

794,844 (now U.S. 1-2 Hi9 Friction Drive Fluid-Ir} N. Duling 3,608,323? issued and Frederick P. Glazier. 9-287l 812,516 (new U.S. 2-19-69 Catalytic Hydrofinishing of Petroleum Distillates in the Lubricating Oil Boiling Range-Ivor W. Mills- Merritt 0. Kirk, Jr. and Albert T.

Olenzak 3,619,414, issued 11971 1 7 BACKGROUND OF THE INVENTION As have been reported by R. L. Kostelak in Lubrication, vol. 56, No. 4, 1970 (pg. 49 et seq.), the principle of operation of the conventional differential in todays American automobile remains the same as the Pecquer differential, invented in 1827. Although this conventional differentia generally performs very satisfactory, it has one serious shortcoming; namely, stalling, which occurs when either rear wheel loses traction. Due to the kinematics of the conventional differential design, the driving torque is divided equally between the two rear wheels and is limited by the wheel with the least traction. Hence, when one wheel loses traction, the vehicle does not move.

To prevent this shortcoming, engineers have developed many ingenious ideas and mechanisms. Each manufacturer has his own descriptive name for his particular mechanism; for example, Chevrolet Positraction, Chrysler Sure-Grip, and Ford Traction-Lek. Generally, however, a differential incorporating one of these mechanisms is called a looking or limited slip or controlled-slip differential.

The limited slip differential used in the American passenger car is essentially the same as a conventional differential except for the incorporation of some form of friction members (e.g. clutch plates or friction cones). The Kostelak article describes the conventional differential and typical controlled-slip differential.

Another pertinent article is Lubricants for Limited Slip Differentials by John W. Allen, given at Fuels and Lubricants Meeting, Society of Automotive Engineers, Houston, Tex., Nov. 1-3, 1966.

SUMMARY OF THE INVENTION In a combination of a controlled-slip differential and a lubricant therefor, we have discovered an improvement wherein said lubricant comprises (A) synthetic sulfurized oil comprising a sulfurized blend of lard oil and a C C monoolefin and (B) a hydrocarbon base stock having a kinematic viscosity at 210 F. in the range of 1.5-200t0 cs., said base stock containing a blend of at least one C C naphthene and from 0.1-20 parts by weight, based on said naphthene, of at least one member from at least one of the following groups (a), (b), (c) and (a) a synthetic liquid C -C olefin homopolymer copolymer, or terpolymer;

(b) a member from group (a) above which is at least partially hydrogenated (preferably, to an iodine number less than 20, more preferably less than 5 and/or having a 195 UVA less than 2.0);

(c) a severely hydrorefined naphthenic lube containing less than 1% of gel aromatic hydrocarbons; and

(d) a severely hydrorefined paraffinic lube containing less than 1% of gel aromatic hydrocarbons;

and wherein the amount of said blend which is present in said base stock is sufiicient to provide a greater coefiicient traction, measured at 600 ft./min., 200 F., 400,000 p.s.i.,

than would be provided by substitution of the same amount of ASTM Oil No. 3 for said blend in said base stock. The preferred lubricant has a viscosity in the range of 5-50 cs. at 210 F., (typically 10-20 cs.), has a chan nel point below 32 F. (more preferred below 10- F.,

typically 0 to --25 F.) and also contains an extreme pressure (EP) additive (e.g. tricresyl phosphate, zinc dithiophosphate, etc.)and an additive which lowers the static friction of the lubricant (e.g. a surface-active, organic phosphate ester of a linear aliphatic, ethoxylated alcohol). I I

Preferably, the C -C naphthene tion temperature in the range of to 30 C. and contains as a structural nucleus, a cyclohexyl hydrindan,

has a glass transi-.

d'itcyeieheiiylr airingaminating 's' iredecane, A spiro pentane, perhydrofluorene, .fierhydrobiphenyl, perhydroterphenyl, decaline, norbornane, .perhydroindace ne, perhydrohomo'tetraphthene; perhydrdacenaphthene; perhydrophenanthrene, 1 'pe'rhydrocry-sem, perhydroindanelspirocyclohexane, perhydrocarylophyllene, pin'a'ne, Y camphane, perhydrophenylnaphthalene Eon perhydropyrene.

'Iheseblended hydrocarbon base stocksare described in theaforementioned applications of Duling etal. ASTM Oil No. 3 is described, for example, in U.S. 3,598,740. Naphthenic and paraffinicoils are described, for'example, in Bruins, P. F. Plasticizer Technology, pages 79, 80 and 85, Vol. 1, Reinhold Pub., N.Y. 1965.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing is an illustration of a controlled-slip differential and will be referred to with reference to a test method for comparing the dynamic torque obtained from a given combination of lubricant and controlled-slip differential. The test can be useful in comparing various lubricants in a given differential.

For example, in a limited slip differential (LSD), the contact plates can be surfaced with swirl patterns to produce high friction. When the plate has become worn, the friction drops drastically and the LSD fails to perform any better than a conventional differential. With a high traction-LSD fluid, the friction property is inherent in the fluid itself and is not completely dependent on the patterned contact surfaces. Thus, the lubricated contacts can have high friction (or traction) even when badly worn.

With reference to the Figure, torque measurements are made by attaching a belt around one of the rear wheels 8 and connecting the belt end to a calibrated spring scale 11. The other rear wheel 1 is then turned by hand to slip the differential. The measurement when slip begins is taken as the break-free torque. A second measurement is determined at approximately 40 rpm. (with the wheel 1 being driven by a motor).

The differential in the Figure consists of a ring gear 4, a differential pinion 6 and cross shaft, and a right 7 and a left 2 clutch plate attached to the differential case. The wheels are connected to the differential pinion by the right 5 and left 3 side gears. Clutch plates are also attached to the left and right axle shafts. The differential assembly and the lubricant are contained in a housing 9.

EXAMPLE I 466 g. of a commercial a-methyl styrene polymer, obtained by conventional acid-catalyzed polymerization, is placed in a one-liter round bottomed flask, attached to a one-inch column, and dry-distilled with essentially no reflux or fractionation at a pot temperature of about 290 C., and a vapor temperature of about 210 C. under a vacuum of about 6 millimeters of mercury. 373 g. of distillate are obtained and about 73 grams of material remain in the bottom of the flask at the end of the distillation. The commercial a-methyl styrene polymer has a softening point of 210 F., a Gardner-Holdt viscosity of J -L, a specific gravity of 1.075, a refractive index at C. of 1.61, a molecular weight of 685, an iodine number of 0, an, acid number of ,0, and asaponification number of 0. L

' EXAMPLE -II 300 g. of the distillation product of Example I is placed in a 316 stainless "steel bomb along with 7.5 grams of Kidney nickel catalyst and the bomb is pressured to 3000 pis.i.g. of 100% hydrogen while'heat is applied until hours at which time the bomb is slowly cooled to ambient temperature while maintaining the hydrogen pressure at 300o*p-.sai; in order to avoid dehydrogenation of the hydrogenated product. The resulting perhydrogenated Bl'y G rTiEthyI' styrene) 611" is topped 'to remove components boiling below 125 i C. The remaining perhydrogenated naphthene product has a KV of 11.07 cs. and a KV of 327.8 cs Analysis by nuclear magnetic resonarrge ghll vlkk shpwsitheoil of this example to consit o" ly liy'dr'indan form), and

A brand of two commercially gav'ailable I polybut' ene polymers (i.e. vol. percentIndapol 'L 1 00and 10% Oronite Special 6) is completely hydrogenated to produce a hydrogenated polybutene 'oil' which analyzes- 0,5 mole percent olefin by the ultraviolet absorbence method. The hydrogenation is at 200 ,C., 2000 p.s.i. of hydro gen for 6 hours usingHarshaw NI0104Pcatalyst. The reresulting hydrogenated polyolefin' oil has a KV of CS. and a Kv oo A i EXAMPLE IV A blended base oil was compounded from 61.0,volumes of the naphthene product. of Example .I I and.33.1 volumes of the hydrogenated polyolefin oil of Example II=I. Then 5.9 volumes of a commercial filimitedslip axleqadditive (Lubrizol Company, Anglamol=99LS was-added-to'the blend to produce a formulated lubricantLTable 1 describes typical properties of Anglamol 99' LS.

TABLE 1 'I Specific gravity 60- F., (15.6" C.)'

Pounds per gallon 60 R, US. --8.79 Pounds per gallon 60 F., IMP. 10.55 Viscosity 210 F., (989 C.) SUS "60 Viscosity 210 F., cst. L .LL L. 10.2

Weight Percent of:

- Typical Sulfur 29.2 Phosporus 2.0

Volume KVn'cPi KViuoF. percent Component (e.'s.)- (e.s.)

7.0 Hydrogenated Cosden SE06 polybutene 11. 04 124 28.0 Hydrogenated Qosden S1115 polybutene 33.5 744 31.6.. Hydrogenated lya-methyl styrene 23 2, 463 .0 d 4.65" 39.6

1:0: "I: Ultra'phos 11, (low static modifier) 1.0.. Synthetic sulfurized 011 The use inthis lubricant of high and low viscosity fractions of the naphthene and paraffin is an. example of dumbell-blendingf. to improve viscosity index.

The ultraphos 11 additive is a surface-active, organic phosphate ester of a linear aliphatic, ethoxylated alcohol.

The synthetic sulfurized oil is the invention of Alexander D. Rechhuite and will be the subject of a later filed application. This oil can be used as a replacement for sulfur'iged sperm oil and can be made'by heating sulfur and ablend'of from 50-95%"lard'dil and 50 of one or a 'r'nixture' of C 'C acyclicrnonoolefin. For example, 10 weight percent of sulfur was added at 250 F. to 90 weight percent of a blend of 85 volumes of lard oil (extra winter strained) and 15 volumes of Chevron CCz0 a-olefin. The sulfur-containing mixture was heated -to 375 F. and maintained at that temperature, with stirring, for 2 hours, then cooled to 200 F., and, finally, blown with air for 1-hour.

Another procedure for making the synthetic sulfurized oil is to heat the large oil-olefin blend to about 300 F., and add sulfur: (e.g. 525%) over a 30 minute period (with agitation), then bring the temperature to 335 F., maintain for /2. ho'ur,-raise the temperature to 375 F. and

time in a high traction-LSD fluid. This results in longer LSD fluid life before chatter occurs.

EXAMPLE VII maintain for 1 hour (also with agitation),-cool to 200 F. 10 was improved when lubricated by the blended tractionand blow with (at 200 F.) for 16 hours.

LSD lubricant. I

TABLE 3.TORQUE THROUGH VARIOUS LIMITED SLIP DIFFERENTIALS Odometer Torque, lbs. Odometer at torque at fluid Car Fluid test Break-free -40 r.p.m. change Chem, 1969 On'ginal 11, 151 20 10 11, 151 Petroleum-LSD-.. fi, 22-52 11, 437 111539 20 21-22 IIIIIIIIIIII Chev. 1969 Origin l 12, 808 22-25 6-9 12, 808

' Petroleum-LSD 13, 239 20-25 13, 274 20 Traction-LSD 13, 309 20 13, 762 19 Pontiac 1970 Original 5', 721 Petroleum-LSD 6, 578 30-32 Traction-LSD.. Ford, 1968- Original 18, 617 90 Petroleum-LSD 1g, 80-32 Traction-LSD 191244 75 The channel point of a lubricant is determined by drawing a channel with a spatula in a sample of lubricant, at a given temperature, and finding the maximum temperature where the walls of the channel no longer cave-in.

' EXAMPLE VI A well-worn limited slip differential in a 1965 Buick Skylark (driven over 65,000 miles) was used to compare lubricants, by the previously described method.

The used, original fill ,fluid was replaced with a fresh conventional petroleum-based LDS fluid (e.g. solvent refined paraffinic lube plus Anglamol 9918). Torque measurements were made periodicallyfor the next 500 miles. Fort the last 100 miles, a 6 p.s.i. difference in air pressure in the rear tires caused the differential to slip constantly. It was believed.that this tire pressure difference caused the fresh fluid to Work into the contact areas. At the end of 500 miles, the conventional fluid was replaced with the blended traction-LSD fluid of Example TV, which had the same viscosity at 100 F. and the same additive system as the petroleum-LSD fluid. After 40 miles of driving with the 6 p.s.i. air pressure differential in the rear tires, the torque measurement at the low speed dynamic conditions was nearly double that observed when the petroleum-LSD fluid was used. There was little difference in the break-free torque since the static friction is primarily dependent on the addtive system. Table 2 presents the test data obtained from this testing.

TABLE 2.-TORQUE THROUGH WORN LIMITED SLIP DIF- FE RENTIAL Torque (1bs.)

The high dynamic friction also helped reduce chatter. With high dynamic friction, static friction can increase to a higher level before chatter will occur. Thus, low static modifying additives are effective for a longer period of Any of the usual gear lube additives can be used in the lubricant-differential combination of the present invention; however, especially beneficial results are obtained when 0.25-10% (based on the base stock) Ultraphos 11 (or less preferred, Ultraphos 12) used as one of the additives. Ultraphos 11 is marketed by Witco Chemical Company and has the following typical properties:

Kv21d==23.44 CS.

KV10Q=217.20 CS- Melting Point=0 C.

Glass Transition Temperature=62 C. ASTM- I: 142

Elemental Analysis:

Carbon: 58.16% Hydrogen: 10.47% Oxygen: 20.44% Ash: 1.58% Phosphorous: 5.77% Sulfur: 0.4% (Schoniger) Nitrogen: 0.10% Chlorine: 10 p.p.m.

Alternatively, Antara LB400 (General Aniline and Film) can be used instead of Ultraphos a sa low static modifier. Another useful, multipurpose additive package which is useful in such lubricants is 2-15 Anglamol 93, which has been previously described and which is a product of Lubrizol Company and comprises a mixture of zinc phosphorodithioate and chlorinated hydrocarbons, a typical analysis being 3% Zn, 3% P, 16.5% C1 and 16.0% S.

The blended fluids and limited slip differential lubricants referred to herein, especially that of Example IV can be used to increase traction between two rolling elements. When traction fluid is used to lubricate high speed ball bearingsfor an example, the main shaft bearings in a turbine engine-it reduces ball skidding. Ball skidding is one of the factors limiting shaft speed. Accordingly, such lubricants can be used for high speed and highly loaded bearings. They can also be used for lubrication ofoverrunning clutches.

During engagement, there is a sliding motion between the cam or rollers and the races in overrunning clutches. Since wear occurs during the engagement period, a lubricant which reduces engagement time will reduce wear and extend service life. In one test, engagement was-reduced from 11 to 2 revolutions simply by replacing the conventional petroleum oil grease with a grease component of a naphthene-paraffin blend similar to that of Example-IV. The traction fluid and its grease show the greatest advantage in clutches 'where load is high enough to elastically deform the rollers or cams. The invention claimed is: 1.'A composition comprising (A) friction improving amounts of a synthetic cosulfurized blend of lard oil and a C C monoolefin and (B) major amounts of a hydro carbon base stock having a kinematic viscosity at 210 F. in the range of 1.5 to 200.0 cs. and consisting essentially of a blend of at least one C C naphthene and from 0.1 to 20 parts by weight, based on said naphthene, of at least one member from at least one of the following groups and (a) a synthetic liquid C -C olefin homopolymer;

(b) a member from group (a) above which is at least partially hydrogenated;

(c) a severely hydrorefined naphthenic mineral lube oil containing less than 1% gel aromatic hydrocarbons; and

(d) a severely hydrorefined paraffinic mineral lube oil containing less than 1% of gel aromatic hydrocarbons;

wherein the amount of said blend of naphthene and member of groups (a), (b), (c) and (d) which is present in said base stock is suflicient to provide a greater coefficient of traction, measured at 600 feet per minute, 200 R, 400,000 p.s.i., than would be provided by substitution of the same amount of ASTM Oil No. 3 for said blend in said base stock, and wherein said composition contains in the range of 0.5 to 10 volume percent of said cosulfurized blend for each 100 volumes of said blended hydrocarbon base stock.

2. The composition of Claim 1 wherein said C C naphthene has a glass transition temperature in the range of 90 to 30 C. and contains, as a structural nucleus, a cyclohexyl hydrindan, di(cyclohexyl)alkane, adamantane, spirodecane, spiropentane, perhydrofluorene, perhydrobiphenyl, perhydroterphenyl, Decalin, norbornane, perhydroindacene, perhydrohomotetraphthene, perhydroacenaphthene, perhydrophenanthrene, perhydrocrysene, perhydroindane 1 spirocyclohexane, perhydrocarylophyllene, pinane, camphane, perhydrophenylnaphthalene or perhydropyrene, and wherein said synthetic sulfurized oil is a sulfurized blend of 50-90 volume percent lard oil and 50-5 volume percentof one or a--mixtureofYC 2 C monoolefin. g

3. The composition of Claim 2 wherein said synthetic 'sulfurized oil'contains in the range of 5-25 weightJpercentsulfur. a

4. The composition. of Claim 1 whereinsaid lubricant also contains an extreme. pressure additiveandran additive which lowers the static friction of said lubricantma 5. The composition of Claim. 4 .wherein said,extr.m pressure additive contains a chlorinated hydrocarbon,.- or a zinc phosphorodithioate or a mixture thereof.

6. The composition of Claim 1 wherein said naphthene is the hydrogenated dimers and trimers of alphamethylstyrene.

7. The composition of Claim 6 wherein said blend contains from 0.1 to 20 parts by weight, based on said naphthene, of a hydrogenated homopolymer of a C monoolefin.

8. The composition of Claim 7 wherein said C olefin consists essentially of isobutylene.

9. The composition of Claim 1 wherein said C C olefin is at least one Q; olefin.

10. The composition of Claim 1 wherein said kinematie viscosity at 210 F. is in the range of 5 to 50 cs. and wherein the channel point is at least 10 F.

11. In the art of lubrication of a controlled-slip differential, the improvement wherein the composition of Claim 1 is used as a lubricant.

References Cited UNITED STATES PATENTS OTHER REFERENCES-'1 r 1 Rounds: Jour. Chem. & 'Eng'.-Data, vol'. 5,-No; 4, 1960, pp. 499-507. r

WARREN H. CANNON, Primary Examiner r 

